Aggregated carrier synchronization and reference signal transmitting and receiving methods, devices and systems

ABSTRACT

A node of a wireless network transmits information to a user equipment over an aggregated carrier that includes a primary carrier having a first set of primary carrier time/frequency resources and a secondary carrier having a second set of secondary carrier time/frequency resources. Synchronization signals and/or reference symbols are transmitted to the user equipment on the secondary carrier less often than on the primary carrier. An indication of when and/or how often the synchronization signals and/or reference symbols will be transmitted to the user equipment on the secondary carrier may also be transmitted to the user equipment over the primary carrier. By transmitting synchronization signals and/or reference symbols to the user equipment on the secondary carrier less often than on the primary carrier, resources of the secondary carrier may be conserved, energy efficiency of the secondary carrier may be increased, and/or interference with other cells may be reduced or prevented.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. non-provisional patent application is a continuation of U.S.patent application Ser. No. 15/426,658, filed Feb. 7, 2017, which itselfis a continuation of U.S. patent application Ser. No. 15/067,432, filedMar. 11, 2016 (now U.S. Pat. No. 9,572,162), which itself is acontinuation of U.S. patent application Ser. No. 13/307,835, filed Nov.30, 2011 (now U.S. Pat. No. 9,629,156); which claims the benefit of U.S.provisional Patent Application No. 61/522,735, filed Aug. 12, 2011,entitled Synchronization and Reference Signals on Aggregated Carriers,the disclosures of all of which are hereby incorporated herein byreference as if set forth fully herein.

TECHNICAL FIELD

Various embodiments described herein relate to radio frequencycommunications and, more particularly, to wireless communicationnetworks and devices, and methods of operating the same.

BACKGROUND

Wireless communication networks are increasingly being used for wirelesscommunications with various types of wireless user equipment. Thewireless network itself may include a plurality of space-apart wirelessbase stations, also commonly referred to as “base stations”, “radioaccess nodes”, “RAN nodes”, “NodeBs”, “eNodeBs” or simply as “nodes”,that define a plurality of cells, and a core network that controls thebase stations and interfaces the base stations with other wired and/orwireless networks. The nodes may be terrestrial and/or space-based. Thenodes communicate with wireless User Equipment (UE), also referred to as“user equipment”, “wireless terminals” or “mobile stations”, using radioresources that are allocated to the wireless network. The radioresources may be defined in terms of time (for example, in a TimeDivision Multiple Access (TDMA) system), frequency (for example, in aFrequency Division Multiple Access (FDMA) system) and/or code (forexample, in a Code Division Multiple Access (CDMA) system). The nodesmay use licensed and/or unlicensed frequency spectrum. Radio resourcesmay be assigned to UEs by the wireless network upon initialcommunication and may be reassigned due to, for example, movement of theUEs, changing bandwidth requirements, changing network traffic, etc.

In many existing wireless cellular communication systems and methods,pilot symbols are transmitted for each antenna or antenna port overradio resource elements that are non-overlapping in time and infrequency with those pilot symbols transmitted for other antennas orantenna ports. For example, in the current release (Rel-10) of Long TermEvolution (LTE) wireless technology, known Reference Symbols (RSs) orpilot symbols are transmitted at various time instants and frequenciesfor different antenna ports. Using these known RSs, a receiver canestimate the channel response from each transmit antenna to each receiveantenna across various times and frequencies.

Moreover, in many existing wireless cellular systems, synchronizationsignals are also transmitted by nodes in order to allow a UE to find andacquire synchronization to a cell within a radio access network. Forexample, in the current release (Rel. 10) of LTE, two special signalsare transmitted on the LTE downlink: a Primary Synchronization Signal(PSS) and a Secondary Synchronization Signal (SSS). The PSS and SSS mayhave similar structure, but the time-domain positions of thesynchronization signals within a frame may differ somewhat depending onwhether the cell is operating in Frequency Division Duplex (FDD) or TimeDivision Duplex (TDD) mode. In the case of FDD, the PSS is transmittedwithin the last symbol of the first slot of subframes 0 and 5, while theSSS is transmitted in the second last symbol of the same slot (i.e.,just prior to the PSS). In contrast, in the case of TDD, the PSS istransmitted within the third symbol of subframes 1 and 6, while the SSSis transmitted in the last symbol of subframes 0 and 5 (i.e., threesymbols ahead of the PSS). Once the UE has detected and identified thePSS of the cell, it has found the timing of the cell and the position ofthe SSS, which has a fixed offset relative to the PSS, along with thecell identity within a single identity group. From the SSS, the UE mayfind the frame timing and the cell identity group. The PSS and SSS arecollectively referred to herein as “synchronization signals”.

LTE allows the aggregation of multiple carriers to send signals betweena node and user equipment. The aggregation of carriers in this manner isshown pictorially in FIG. 1. The main carrier is referred to as aprimary carrier while the additional carrier is referred to as asecondary carrier. In Rel-10 of LTE, the secondary carrier is generallyrequired to have the features of a regular LTE carrier. That is, itcarries synchronization signals for time and frequency synchronization,reference symbols for channel estimation and control signals for dataallocations and other control functions much like the primary carrier.

The reuse of carrier frequencies across multiple sites within a cellularnetwork may give rise to interference issues. Additionally,synchronization and reference signals transmitted by nodes in thenetwork may also be wasteful of energy. Interference issues may beespecially problematic in so-called “heterogeneous networks” wherecarrier aggregation is accomplished using micro or pico base stations.

The approaches described in this section could be pursued, but are notnecessarily approaches that have been previously conceived or pursued.Therefore, unless otherwise indicated herein, the approaches describedin this section are not prior art to claims in this application and anyapplication claiming priority from this application, and are notadmitted to be prior art by inclusion in this section.

SUMMARY

Various embodiments described herein operate a node of a wirelessnetwork by transmitting information to a user equipment over anaggregated carrier that includes a primary carrier that comprises afirst set of primary carrier time/frequency resources and a secondarycarrier that comprises a second set of secondary carrier time/frequencyresources. Synchronization signals and/or reference symbols aretransmitted to the user equipment on the secondary carrier less oftenthan on the primary carrier. In some embodiments, an indication of whenand/or how often the synchronization signals and/or reference symbolswill be transmitted to the user equipment on the secondary carrier isalso transmitted to the user equipment over the primary carrier. Bytransmitting synchronization signals and/or reference symbols to theuser equipment on the secondary carrier less often than on the primarycarrier, resources of the secondary carrier may be conserved, energyefficiency of the secondary carrier may be increased, and/orinterference with other cells may be reduced or prevented.

Various embodiments can be provided to transmit synchronization signalsand/or reference symbols to the user equipment on the secondary carrierless often than on the primary carrier. For example, in someembodiments, the secondary carrier comprises a second set of secondarycarrier time/frequency resources that are synchronized in time andfrequency with the first set of primary carrier time/frequencyresources. In these embodiments, the node refrains from transmitting thesynchronization and/or reference signals to the user equipment on thesecondary carrier that comprises a second set of secondary carriertime/frequency resources that are synchronized in time and frequencywith the first set of primary carrier time/frequency resources. In someembodiments, the second set of secondary carrier time/frequencyresources are synchronized in time and frequency with the first set ofprimary carrier time/frequency resources, but are offset therefrom by aconstant time offset and/or constant frequency offset, and an indicationof the constant time offset and/or the constant frequency offset istransmitted to the user equipment over the primary carrier. Theindication of the constant time offset and/or the constant frequencyoffset may be transmitted to the user using a Radio Resource Control(RRC) message over the primary carrier, wherein the RRC message includesa parameter that provides the indication of the constant time offsetand/or the constant frequency offset. Moreover, when the primary carrierand the secondary carrier are co-sited, the node can refrain fromtransmitting synchronization signals and reference symbols to the userequipment on the secondary carrier.

In other embodiments, the secondary carrier comprises a second set ofsecondary carrier time/frequency resources that are synchronized in timewith the first set of primary carrier time/frequency resources, but arein a different frequency band than the first set of primary carriertime/frequency resources. The primary carrier and the secondary carriermay be co-sited. In these embodiments, the reference symbols aretransmitted to the user equipment on the secondary carrier less often onthe primary carrier. Moreover, in some embodiments, the node refrainsfrom transmitting synchronization signals to the user equipment on thesecondary carrier. In some embodiments, an indication of when thereference symbols will be transmitted to the user equipment on thesecondary carrier is transmitted by the node to the user equipment overthe primary carrier. Moreover, in some embodiments, the referencesymbols are transmitted to the user equipment on the secondary carrierat a periodicity that is lower than that of the primary carrier, and anindication of the periodicity (i.e., how often) is transmitted to theuser equipment over the primary carrier.

In still other embodiments, the secondary carrier comprises a second setof time/frequency resources that are not synchronized in time with thefirst set of primary carrier time/frequency resources and are also in adifferent frequency band than the first set of primary carriertime/frequency resources. The primary carrier and the secondary carriermay not be co-sited. In these embodiments, the synchronization signalsand the reference symbols are transmitted to the user equipment on thesecondary carrier less often than on the primary carrier. Moreover, atleast one indication of when and/or how often the synchronizationsignals and/or the reference symbols will be transmitted to the userequipment on the secondary carrier is transmitted by the node to theuser equipment over the primary carrier. In some embodiments, both thesynchronization signals and the reference symbols are transmitted to theuser equipment on the secondary carrier at a periodicity that is lowerthan that of the primary carrier, and at least one indication of theperiodicity of transmitting the synchronization signals and/or thereference symbols is transmitted from the node to the user equipmentover the primary carrier. In some embodiments, the at least oneindication is transmitted over the primary carrier as a parameter of anRRC message.

Various embodiments have been described above primarily in connectionwith methods of operating a node of the wireless communications network.However, other embodiments can provide the node itself. The nodecomprises at least one transmitter that is configured to transmitinformation to a user equipment over an aggregated carrier that includesa primary carrier that comprises a first set of primary carriertime/frequency resources and a secondary carrier that comprises a secondset of secondary carrier time/frequency resources. The at least onetransmitter may be further configured to transmit synchronizationsignals and/or reference symbols to the user equipment on the secondarycarrier less often on the primary carrier, according to any of theembodiments that were described above.

Moreover, other nodes of a wireless communication network may beprovided according to other embodiments described herein. In theseembodiments, the at least one transmitter is configured to transmitinformation to a user equipment over an aggregated carrier that includesa primary carrier that comprises a first set of primary carriertime/frequency resources and a secondary carrier that comprises a secondset of secondary carrier time/frequency resources. The at least onetransmitter is further configured to transmit synchronization signalsand/or reference symbols to the user equipment over the primary carrier.The at least one transmitter is still further configured to transmit tothe user equipment over the primary carrier, information aboutsynchronization signals and/or reference symbols of the secondarycarrier. The information may comprise an indication of when thesynchronization signals and/or the reference symbols will be transmittedto the user equipment on the secondary carrier and/or an indication of aperiodicity (i.e., how often) of transmitting the synchronizationsignals and/or the reference symbols to the user equipment on thesecondary carrier. Analogous methods of operating a node may also beprovided according to various embodiments described herein.

Various other embodiments described herein may provide methods ofoperating a user equipment of a wireless communications network. Thesemethods may include receiving information over an aggregated carrierthat includes a primary carrier that comprises a first set of primarycarrier time/frequency resources and a secondary carrier that comprisesa second set of secondary carrier time/frequency resources.Synchronization signals and/or reference symbols may also be receivedover the primary carrier, and the synchronization signals and/orreference symbols that were received over the primary carrier may beprocessed. Moreover, synchronization signals and/or reference symbolsare received over the secondary carrier less often than on the primarycarrier. The synchronization signals and/or the reference symbols thatwere received over the secondary carrier less often than the primarycarrier are also processed by the user equipment.

These methods of operating a user equipment may further includereceiving over the primary carrier an indication of how often thesynchronization signals and/or reference symbols will be received on thesecondary carrier. The indication may include at least one indication ofwhen the synchronization signals and/or the reference symbols will bereceived on the secondary carrier and/or at least one indication of aperiodicity (i.e., how often) of receiving the synchronization signalsand/or the reference symbols on the secondary carrier. The at least oneindication may be received over the primary carrier as a parameter of anRRC message. Moreover, analogous user equipment may also be providedthat includes at least one transmitter that is configured to receiveinformation over an aggregated carrier that includes a primary carrierthat comprises a first set of primary carrier time/frequency resourcesand a secondary carrier that comprises a second set of secondary carriertime/frequency resources. The transmitter may also be further configuredto receive and process the synchronization signals and/or referencesymbols over the primary carrier and to receive and processsynchronization signals and/or reference symbols over the secondarycarrier less often than on the primary carrier, as was described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 conceptually illustrates an aggregated carrier in Release 10(Rel-10) of LTE.

FIG. 2 is a flowchart of operations that may be performed to operate anode of a wireless communications network according to variousembodiments described herein.

FIG. 3 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tovarious embodiments described herein.

FIG. 4 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that are configured, forexample, as illustrated in FIG. 3.

FIG. 5 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tovarious other embodiments described herein.

FIG. 6 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that are configured, forexample, as illustrated in FIG. 5.

FIG. 7 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tostill other embodiments described herein.

FIG. 8 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that are configured, forexample, as illustrated in FIG. 7.

FIG. 9 is a flowchart of operations that may be performed by a nodeaccording to yet other embodiments described herein.

FIG. 10 is a flowchart of operations that may be performed by a userequipment of a wireless communications network according to variousembodiments described herein.

FIG. 11 is a block diagram of a wireless network according to variousembodiments described herein.

FIG. 12 is a block diagram of a user equipment according to variousembodiments described herein.

FIG. 13 is a block diagram of a node according to various embodimentsdescribed herein.

DETAILED DESCRIPTION

Various embodiments described herein transmit synchronization signalsand/or reference symbols from a node to user equipment on a secondarycarrier of an aggregated carrier less often than on the primary carrierof the aggregated carrier. Moreover, an indication of when and/or howoften the synchronization signals and/or reference symbols will betransmitted to the user equipment on the secondary carrier may also betransmitted by the node to the user equipment over the primary carrier.The user equipment may receive and process synchronization signalsand/or reference symbols over the primary carrier and may also receivesynchronization signals and/or reference symbols over the secondarycarrier less often than on the primary carrier, and process thesesynchronization signals and/or reference symbols.

Various embodiments described herein may arise from a recognition thatin the current release of LTE, the secondary carrier is generallyrequired to have the features of the regular LTE carrier. That is, itcarries synchronization signals for time and frequency synchronization,reference symbols for channel estimation and control signals for dataallocations and other control functions, much like the primary carrier.In future releases of LTE, however, it is proposed to allow thesecondary carrier to have non-backward compatible features. Therefore,changes could potentially be made as to how synchronization signals andother signals are transmitted on the secondary carrier.

Moreover, various embodiments described herein may also arise fromrecognition that LTE can be deployed in multiple ways. In one type ofdeployment, most of the base stations in the network are so-called macrobase stations and have similar transmit powers and antenna gains. Inanother type of deployment, commonly referred to as heterogeneousnetworks, there may be two or more tiers of base stations, with the maintier being a set of macro base stations and the secondary tiers beingmicro and/or pico base stations. The micro and pico base stationstypically have lower transmit powers and therefore smaller cell ranges.With judicious placement of pico and micro cells, the overall networkcapacity can be increased.

Various embodiments described herein may also arise from recognitionthat, under low load conditions, i.e., when there are very few UEsreceiving data, most of the signals transmitted in the network arecontrol signals such as synchronization signals and reference symbols.Under low load conditions, the interference among these signals frommultiple sites may limit system capacity. The challenges in deployingheterogeneous networks often revolve around such interference betweenthe macro and micro/pico layers of the network. In many cases thereception of synchronization and reference signals transmitted from apico base station is inhibited due to interference from similar signalsat the macro base station. Thus, even though data could be received fromthe pico base station, the interference on synchronization and othersignals may impede reception of data at the UE from the pico basestation.

Energy efficiency of broadband wireless networks is also becomingincreasingly important. In some scenarios, about 90% of the energy in awireless network is consumed when no user is receiving data. Variousembodiments described herein may also arise from recognition that theperiodic transmission of synchronization and reference signals from abase station, even when no users are in the system, is one of the keycontributors to power consumption in LTE networks.

Given the issues of energy efficiency and interference with currenthomogeneous and heterogeneous LTE networks, various embodimentsdescribed herein can provide synchronization signals and referencesymbols for secondary carriers in a carrier aggregation situation, whilemitigating one or more of the issues listed above, and/or other issues.Reference symbols for channel estimation purposes can be transmittedwithin data allocations that are made to a UE to transfer control ordata messages in order to combat one or more of the of the above issues.

Existing solutions for synchronization signals and reference symbolsthat are intended to be used by multiple UEs generally use some form ofperiodic transmission. That is, these signals/symbols appear at regularintervals, and the UEs in the system use knowledge of the periodicityfor various purposes including deriving frame timing and maintainingtime and frequency synchronization. Various embodiments described hereinmay arise from recognition that a problem with such solutions is thatthe periodic transmission of these signals occurs whether there are anyUEs that are attempting to use the signals/symbols. This can lead toenergy inefficiency as well as unnecessary interference to other cells,whether in a homogeneous or heterogeneous deployment.

Various embodiments described herein address the transmission ofsynchronization and reference signals on a secondary carrier in acarrier aggregation deployment where a primary carrier is also beingtransmitted. In some embodiments, it is assumed that the primary carrieris an LTE compliant carrier with synchronization and reference signalsbeing transmitted with the periodicity as defined in the LTEspecifications.

Various embodiments described herein can overcome one or more of theissues described above, for example, by avoiding transmission ofsynchronization signals and/or reference symbols when there are noactive UEs in the system. When UEs are actively using the secondarycarrier, the transmission of these signals/symbols may be signaledexplicitly on the primary carrier. This allows synchronization signalsand reference symbols to be scheduled just like data transmissions. Thismay be contrasted with the current release of LTE, where typically,transmission of such signals/symbols occurs in a fixed manner. Thisflexibility in scheduling or suppressing the transmission of thesesignals/symbols can lead to an increased ability to manage interferencein the network during low load conditions, which can increase systemperformance. It can also allow the wireless network to be more energyefficient.

FIG. 2 is a flowchart of operations that may be performed to operate anode of a wireless communications network according to variousembodiments described herein. Referring to FIG. 2, at Block 210, a nodeof a wireless communications network can operate by transmittinginformation to a user equipment over an aggregated carrier that includesa primary carrier that comprises a first set of primary carriertime/frequency resources and a secondary carrier that comprises a secondset of secondary carrier time/frequency resources. At Block 220,synchronization signals and/or reference symbols are transmitted to theuser equipment on the secondary carrier less often than on the primarycarrier. Moreover, at Block 230, in some embodiments, an indication ofwhen and/or how often the synchronization signals and/or referencesymbols will be transmitted to the user equipment on the secondarycarrier may also be transmitted to the user equipment over the primarycarrier.

FIG. 3 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tovarious embodiments described herein. The primary and the secondarycarriers may be transmitted from the same cell site (i.e., co-sited) andmay be synchronized in time and frequency. In this scenario, accordingto various embodiments described herein, no synchronization or referencesignals need be transmitted on the secondary carrier. Specifically, asshown in FIG. 3, the primary carrier may transmit a primarysynchronization signal and/or a secondary synchronization signal(PSS/SSS) in a given slot of the primary carrier. Reference Symbols (RS)may also be transmitted as shown. Control messages may also betransmitted including a Radio Resource Control (RRC) message.

The UE obtains initial time and frequency synchronization andsubsequently maintains synchronization using the synchronization signal(PSS/SSS) and/or other reference symbols if available on the primarycarrier. Note that the actual carrier frequencies and frame timings maybe different. This synchronization may be maintained if the offsetbetween the carrier frequencies and frame timings on the primary andsecondary carriers is constant. Knowledge of these constant offsetsallows the UE to operate on the secondary carrier after synchronizationis performed with the primary carrier. The offset parameters may besignaled to the UEs using control signaling on the primary carrier, suchas the RRC message.

Mobility measurements may also be performed by the UE using the PSS/SSS(synchronization signals) or the reference symbols on the primarycarrier. Such measurements are used to determine if a handoff is desiredfrom the current service cell to a different cell. Since the carriersare co-sited, and assuming that the transmitted power spectral densityis the same on both carriers, measurements on the primary carrier aresufficient for a UE not currently on the primary or secondary carrier todecide if it should move to the cell.

FIG. 4 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that are configured, forexample, as illustrated in FIG. 3. Blocks 410-430 of FIG. 4 maycorrespond to the operations of Blocks 210-230 of FIG. 2, respectively,but are performed using the primary and secondary carriers of FIG. 3.

Referring to Block 410, information is transmitted to the user equipmentover the aggregated carrier that includes a primary carrier thatcomprises a first set of primary carrier time/frequency resources and asecondary carrier that comprises a second set of secondary carriertime/frequency resources that are synchronized in time and frequencywith the first set of primary carrier time/frequency resources. At Block420, the node refrains from transmitting synchronization signals and/orreference symbols to the user equipment on the secondary carrier thatcomprises a second set of secondary carrier time/frequency resourcesthat are synchronized in time and frequency with the first set ofprimary carrier time/frequency resources. In some embodiments, at Block430, the second set of secondary carrier time/frequency resources aresynchronized in time and frequency with the first set of primary carriertime/frequency resources, but are offset therefrom by a constant timeoffset and/or a constant frequency offset, and the node can transmit tothe user equipment over the primary carrier, an indication of theconstant time offset and/or the constant frequency offset.

In some embodiments, the indication of Block 430 is transmitted using anLTE RRC message over the primary carrier, that includes a parameter thatprovides the indication of the constant time offset and/or the constantfrequency offset. Finally, in some embodiments of FIG. 4, the primarycarrier and the secondary carrier are co-sited, and the node refrainsfrom transmitting both the synchronization signals and the referencesymbols to the user equipment on the secondary carrier.

FIG. 5 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tovarious other embodiments described herein. Embodiments of FIG. 5 maydiffer from embodiments of FIG. 3 in the fact that the two carriers arein different bands. In such situations, it is possible that thepropagation characteristics of each of the bands are different. Forexample, the primary carrier may be in the 1900 MHz band while thesecondary carrier may be in the 700 MHz band. In such situations, it maybe desirable for mobility measurements to be made on the secondarycarrier itself rather than deriving mobility measurements from theprimary carrier. Thus, as illustrated in FIG. 5, according to variousembodiments described herein, reference symbols are transmitted on thesecondary carrier, and are signaled from the primary carrier, as shown,for example, by “Signaling” of FIG. 5. In other embodiments, thereference symbols are transmitted with a periodicity (for example, everyX number of subframes) that is configurable and is signaled to the UE(s)from the primary carrier, as shown, for example, by “Signaling” of FIG.5.

The UE may obtain time and frequency synchronization as in embodimentsof FIGS. 3 and 4. For mobility measurements, the UE first receivescontrol signaling on the primary carrier indicating that the referencesymbols that can be used for mobility measurements are going to betransmitted on the secondary carrier. The UE then receives the referencesymbols on the secondary carrier and uses them to perform mobilitymeasurements.

The location of the reference symbols in the secondary carrier can beindicated in many ways. For example, in some embodiments, the offsetbetween the time of signaling on the primary carrier and thetransmission of the reference symbols on the secondary carrier (in termsof subframes or OFDM symbols) may be signaled. In other embodiments, thesubframe number on the secondary carrier in which the reference symbolsare going to be transmitted is explicitly included in the signaling.Other techniques may be used.

FIG. 6 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that are configured, forexample, as illustrated in FIG. 5. Blocks 610-630 of FIG. 6 maycorrespond to the operations of Blocks 210-230 of FIG. 2, respectively,but are performed using the primary and secondary carriers of FIG. 5.

More specifically, referring to FIG. 6, at Block 610, information istransmitted to the user equipment over an aggregated carrier thatincludes a primary carrier that comprises a first set of primary carriertime/frequency resources and a secondary carrier that comprises a secondset of secondary carrier time/frequency resources that are synchronizedin time with the first set of primary carrier time/frequency resourcesbut are in a different frequency band than the first set of primarycarrier time/frequency resources. As shown at Block 620 a, referencesymbols are transmitted to the user equipment on the secondary carrierless often than on the primary carrier. Moreover, as shown at Block 620b, synchronization signals are refrained from being transmitted (i.e.,are not transmitted) on the secondary carrier. Finally, as shown atBlock 630, an indication of when and/or how often the reference symbolswill be transmitted to the user equipment on the secondary carrier mayalso be transmitted to the user equipment over the primary carrier. Insome embodiments, at Block 630, the reference symbols are transmitted tothe user equipment on the secondary carrier at a periodicity that islower than that of the primary carrier, and an indication of theperiodicity is transmitted.

FIG. 7 illustrates a frame of a primary carrier and a secondary carrierof an aggregated carrier that is configured to operate according tostill other embodiments described herein. In embodiments of FIG. 7, theprimary and secondary carriers may not be synchronized in time andfrequency or may be transmitted from different sites. In this case,according to various embodiments described herein, both synchronizationsignals and reference symbols are sent over the secondary carrier andare explicitly signaled from the primary carrier when they are sent. Inother embodiments, the synchronization signals and reference symbols aresent periodically over the secondary carrier, with the periodicity beingconfigurable and being signaled by the primary carrier. Theperiodicities of the synchronization signals and reference symbols maybe different.

As shown in FIG. 7, the UE obtains time and frequency synchronization byfirst synchronizing to the primary carrier and receiving signaling onthe primary carrier that indicates the location of the synchronizationsignals and reference symbols on the secondary carrier. The UE then usesthe PSS/SSS sequence on the secondary carrier to perform initialsynchronization or to maintain synchronization. The UE also uses thereference symbols on the secondary carrier when needed for mobilitymeasurements. The signaling of the locations of the secondary carrierreference symbols and/or synchronization signals can be performed, forexample, as was described in connection with FIG. 5.

FIG. 8 is a flowchart of operations that may be performed by a nodeusing a primary and a secondary carrier that is configured, for example,as illustrated in FIG. 7. Blocks 810-830 of FIG. 8 may correspond to theoperations of Blocks 210-230 of FIG. 2, respectively, but are performedusing the primary and secondary carriers of FIG. 7.

Referring to FIG. 8, at Block 810, information is transmitted to theuser equipment over an aggregated carrier that includes a primarycarrier that comprises a first set of primary carrier time/frequencyresources and a secondary carrier that comprises a second set ofsecondary carrier time/frequency resources that are not synchronized intime with the first set of primary carrier time/frequency resources andthat also are in a different frequency band than the first set ofprimary carrier time/frequency resources. At Block 820, synchronizationsignals and reference symbols are transmitted to the user equipment onthe secondary carrier less often than on the primary carrier. In someembodiments, at Block 830, an indication of when and/or how often thesynchronization and/or the reference symbols will be transmitted to theuser equipment on the secondary carrier is transmitted to the userequipment over the primary carrier. Moreover, in some embodiments, thesynchronization signals and the reference symbols are transmitted to theuser equipment on the secondary carrier at a periodicity that is lowerthan that of the primary carrier, and operations of Block 830 transmitto the user equipment over the primary carrier at least one indicationof the periodicity of transmitting the synchronization signals and/orthe reference symbols, to indicate how often transmission will takeplace.

FIG. 9 is a flowchart of operations that may be performed by a node of awireless communications network according to yet other embodimentsdescribed herein. In these embodiments, secondary carriersynchronization signal/reference symbol signaling may be transmittedfrom the primary carrier as was illustrated in FIGS. 5 and 7 for anypurpose.

Referring to FIG. 9, at Block 210, information is transmitted to a userequipment over an aggregated carrier that includes a primary carrierthat comprises a first set of primary carrier time/frequency resourcesand a secondary carrier that comprises a second set of secondary carriertime/frequency resources. At Block 920, synchronization signals and/orreference symbols are transmitted to the user equipment over the primarycarrier. Moreover, at Block 930, information about synchronizationsignals and/or reference symbols of the secondary carrier aretransmitted to the user equipment over the primary carrier. In someembodiments, the information about synchronization signals and/orreference symbols of the secondary carrier comprises an indication ofwhen the synchronization signals and/or the reference symbols will betransmitted to the user equipment on the secondary carrier and/or anindication of a periodicity (i.e., how often) of transmitting thesynchronization signals and/or the reference symbols to the userequipment on the secondary carrier. Finally, in some embodiments, thesynchronization signals and/or reference symbols are transmitted overthe secondary carrier based on the information that was transmitted inBlock 930. The transmission on the secondary carrier may be performed bythe same transmitter that performs the operations of FIG. 9 and/or by adifferent transmitter.

FIG. 10 is a flowchart of operations that may be performed by a userequipment according to various embodiments described herein.Specifically, referring to Block 1010, the user equipment receivesinformation over an aggregated carrier that includes a primary carrierthat comprises a first set of primary carrier time/frequency resourcesand a secondary carrier that comprises a second set of secondary carriertime/frequency resources. At Block 1020, the user equipment receives andprocesses synchronization signals and/or reference symbols over theprimary carrier. At Block 1030, the user equipment receives andprocesses synchronization signals and/or reference symbols over thesecondary carrier less often than on the primary carrier and processesthe synchronization signals and/or the reference symbols that werereceived over the secondary carrier less often than on the primarycarrier. In some embodiments, at Block 1040, the user equipment alsoreceives, over the primary carrier, an indication of when and/or howoften the synchronization signals and/or reference symbols will bereceived on the secondary carrier. In some embodiments, the indicationcomprises at least one indication of when the synchronization signalsand/or the reference symbols will be received on the secondary carrierand/or of a periodicity of receiving the synchronization signals and/orthe reference symbols on the secondary carrier.

FIGS. 5 and 7 illustrated signaling that may be provided according tovarious embodiments described herein, as was described, for example, atBlocks 230, 430, 630, 830, 930 and 1040 herein. Various embodiments ofthis signaling will now be described. For example, signaling describedherein may be performed using one or more parameters of an RRC message,one or more parameters that are signaled by an L1 control channel, usingimplicit signaling and/or using other signaling mechanisms that may beprovided, for example, by LTE.

The RRC message can be provided by a broadcast RRC message and/or adedicated RRC message to each specific UE in that primary cell. When theRRC parameters are sent via broadcast message, the RRC parameters caneither be signaled through one of the System Information Blocks (SIBs)that are transmitted for sending control information or can be includedin the messages sent on the Physical Broadcast CHannel (PBCH) that isreceived by the UEs before receiving information in the SIBs. Also, RRCparameters sent via dedicated messages may be common to all UEs thatutilize the information and are attached to the same cells.

In other embodiments, one or more parameters may be signaled by an L1control channel. In still other embodiments, implicit signaling may beused. The implicit signaling can, for example, be derived based on oneor more of the following applicable parameters: Physical Cell Indicator(PCI), a parameter that defines the transmission point, OFDM symbolnumber, slot number, subframe number, radio frame number, etc. Variousother signaling techniques may be provided, and various embodimentsdescribed herein should not be construed as limited to the abovetechniques.

Various embodiments described herein can enhance energy efficiency. Bysuppressing the transmission of synchronization signals and/or referencesymbols according to various embodiments described herein, energyefficiency can be enhanced. When synchronization signals and/orreference symbols are to be transmitted, the transmission can be eithersignaled and/or their periodicity can be signaled. Such configurabilityallows the system to reduce or minimize transmission of thesesignals/symbols during times of low or no load, thus reducing powerconsumption and increasing energy efficiency.

Moreover, system performance may be improved through interferencemanagement. Specifically, various embodiments described herein can allowsynchronization signals and/or reference symbols to either not betransmitted on the secondary carrier or to effectively be scheduled justlike other data transmissions. This flexibility in scheduling orsuppressing the transmission of these signals/symbols can lead to anincreased ability to manage interference in the network during low loadconditions, thus increasing system performance.

Additional discussion of various embodiments described herein will nowbe provided. Although various embodiments described herein may beimplemented in any appropriate type of telecommunication systemsupporting any suitable communication standards using any suitablecomponents, particular embodiments of the described solutions may beimplemented in an LTE network, such as that illustrated in FIG. 11.

As shown in FIG. 11, an example network 1100 may include one or moreinstances of UEs 1110 and one or more nodes 1120 capable ofcommunicating with these UEs, along with any additional network elements1130 suitable to support communication between UEs or between a UE andanother communication device (such as a landline telephone). Althoughthe illustrated UEs 1110 may represent communication devices thatinclude any suitable combination of hardware and/or software, these UEsmay, in particular embodiments, represent devices such as the example UEillustrated in greater detail by FIG. 12. Similarly, although theillustrated nodes 1120 may represent network nodes that include anysuitable combination of hardware and/or software, these nodes may, inparticular embodiments, represent devices such as the example nodesillustrated in greater detail by FIG. 13.

As shown in FIG. 12, the example UE 1110 includes a UE processor 1210, amemory 1220, a transceiver 1230, an antenna 1240 and a housing 1250. Inparticular embodiments, some or all of the functionality described aboveas being provided by a UE may be provided by the UE processor 1210executing instructions stored on a computer-readable medium, such as thememory 1220 shown in FIG. 12. Alternative embodiments of the UE mayinclude additional components beyond those shown in FIG. 12 that may beresponsible for providing certain aspects of the UE's functionality,including any of the functionality described above and/or anyfunctionality necessary to support the solution described above.

As shown in FIG. 13, the example node 1120 includes a processor 1310, amemory 1320, a transceiver 1340, an antenna 1350 and a housing 1360. Inparticular embodiments, some or all of the functionality described aboveas being provided by a home base station, an HeNB, an HNB, a pico/femtobase station, a base station controller, a node B, an eNB, and/or anyother type of mobile communications node may be provided by the node1120 executing instructions stored on a computer-readable medium, suchas the memory 1320 shown in FIG. 13. Accordingly, a node according tovarious embodiments described herein can include a wireless transceiver1340 that is configured to wirelessly communicate with wireless UserEquipment, such as the wireless User Equipment of FIG. 12, a networkinterface 1330 that is configured to establish a communication path toan element of a network 1130, and a processor 1310. Alternativeembodiments of the node 1120 may include additional componentsresponsible for providing additional functionality, including any of thefunctionality identified above and/or any functionality necessary tosupport the solution described above.

Various embodiments were described herein with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventionto those skilled in the art.

It will be understood that, when an element is referred to as being“connected”, “coupled”, “responsive”, or variants thereof to anotherelement, it can be directly connected, coupled, or responsive to theother element or intervening elements may be present. In contrast, whenan element is referred to as being “directly connected”, “directlycoupled”, “directly responsive”, or variants thereof to another element,there are no intervening elements present. Furthermore, “coupled”,“connected”, “responsive”, or variants thereof as used herein mayinclude wirelessly coupled, connected, or responsive. Like numbers referto like elements throughout. The terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting of the invention. As used herein, the singular forms “a”,“an” and “the” are intended to include the plural forms as well, unlessthe context clearly indicates otherwise. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention.Moreover, as used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of this specification andthe relevant art and will not be interpreted in an idealized or overlyformal sense expressly so defined herein.

Various embodiments described herein can operate in any of the followingRadio Access Technologies: Advanced Mobile Phone Service (AMPS),ANSI-136, Global Standard for Mobile (GSM) communication, General PacketRadio Service (GPRS), enhanced data rates for GSM evolution (EDGE), DCS,PDC, PCS, code division multiple access (CDMA), wideband-CDMA, CDMA2000,Universal Mobile Telecommunications System (UMTS), 3GPP LTE (3^(rd)Generation Partnership Project Long Term Evolution) and/or 3GPP LTE-A(LTE Advanced). For example, GSM operation can includereception/transmission in frequency ranges of about 824 MHz to about 849MHz and about 869 MHz to about 894 MHz. EGSM operation can includereception/transmission in frequency ranges of about 880 MHz to about 914MHz and about 925 MHz to about 960 MHz. DCS operation can includetransmission/reception in frequency ranges of about 1410 MHz to about1785 MHz and about 1805 MHz to about 1880 MHz. PDC operation can includetransmission in frequency ranges of about 893 MHz to about 953 MHz andabout 810 MHz to about 885 MHz. PCS operation can includetransmission/reception in frequency ranges of about 1850 MHz to about1910 MHz and about 1930 MHz to about 1990 MHz. 3GPP LTE operation caninclude transmission/reception in frequency ranges of about 1920 MHz toabout 1980 MHz and about 2110 MHz to about 2170 MHz. Other Radio AccessTechnologies and/or frequency bands can also be used in variousembodiments described herein. All these systems are designed to operatein a variety of bands typically known as the International MobileTelecommunications (IMT) bands that are defined by the InternationalTelecommunications Union-Radio Communication Bureau (ITU-R) and can, ingeneral, be located in frequency ranges between 200 MHz and 5 GHZ withinthe current state of the art. It should, however, be noted that variousembodiments described herein are equally applicable for any radiosystem, and are not restricted in any way to the IMT bands in any way.

For purposes of illustration and explanation only, various embodimentsof the present invention were described herein in the context of userequipment that are configured to carry out cellular communications(e.g., cellular voice and/or data communications). It will beunderstood, however, that the present invention is not limited to suchembodiments and may be embodied generally in any wireless communicationterminal that is configured to transmit and receive according to one ormore radio access technologies.

As used herein, the term “user equipment” includes cellular and/orsatellite radiotelephone(s) with or without a display (text/graphical);Personal Communications System (PCS) terminal(s) that may combine aradiotelephone with data processing, facsimile and/or datacommunications capabilities; Personal Digital Assistant(s) (PDA) orsmart phone(s) that can include a radio frequency transceiver and apager, Internet/Intranet access, Web browser, organizer, calendar and/ora global positioning system (GPS) receiver; and/or conventional laptop(notebook) and/or palmtop (netbook) computer(s) or other appliance(s),which include a radio frequency transceiver. As used herein, the term“user equipment” also includes any other radiating user device that mayhave time-varying or fixed geographic coordinates and/or may beportable, transportable, installed in a vehicle (aeronautical, maritime,or land-based) and/or situated and/or configured to operate locallyand/or in a distributed fashion over one or more terrestrial and/orextra-terrestrial location(s). Finally, the term “node” includes anyfixed, portable and/or transportable device that is configured tocommunicate with one or more user equipment and a core network, andincludes, for example, terrestrial cellular base stations (includingmicrocell, picocell, wireless access point and/or ad hoc communicationsaccess points) and satellites, that may be located terrestrially and/orthat have a trajectory above the earth at any altitude.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,if used herein, the common abbreviation “e.g.”, which derives from theLatin phrase exempli gratia, may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. If used herein, the commonabbreviation “i.e.”, which derives from the Latin phrase id est, may beused to specify a particular item from a more general recitation.

Exemplary embodiments were described herein with reference to blockdiagrams and/or flowchart illustrations of computer-implemented methods,apparatus (systems and/or devices) and/or computer program products. Itis understood that a block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions that are performed by one or more computer circuits. Thesecomputer program instructions may be provided to a processor circuit ofa general purpose computer circuit, special purpose computer circuitsuch as a digital processor, and/or other programmable data processingcircuit to produce a machine, such that the instructions, which executevia the processor of the computer and/or other programmable dataprocessing apparatus, transform and control transistors, values storedin memory locations, and other hardware components within such circuitryto implement the functions/acts specified in the block diagrams and/orflowchart block or blocks, and thereby create means (functionality)and/or structure for implementing the functions/acts specified in theblock diagrams and/or flowchart block(s). These computer programinstructions may also be stored in a computer-readable medium that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable medium produce an article of manufacture includinginstructions which implement the functions/acts specified in the blockdiagrams and/or flowchart block or blocks.

A tangible, non-transitory computer-readable medium may include anelectronic, magnetic, optical, electromagnetic, or semiconductor datastorage system, apparatus, or device. More specific examples of thecomputer-readable medium would include the following: a portablecomputer diskette, a random access memory (RAM) circuit, a read-onlymemory (ROM) circuit, an erasable programmable read-only memory (EPROMor Flash memory) circuit, a portable compact disc read-only memory(CD-ROM), and a portable digital video disc read-only memory(DVD/BlueRay).

The computer program instructions may also be loaded onto a computerand/or other programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer and/or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functions/actsspecified in the block diagrams and/or flowchart block or blocks.

Accordingly, embodiments of the present invention may be embodied inhardware and/or in software (including firmware, resident software,micro-code, etc.) that runs on a processor such as a digital signalprocessor, which may collectively be referred to as “circuitry,” “amodule” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated. Moreover,although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Many different embodiments were disclosed herein, in connection with thefollowing description and the drawings. It will be understood that itwould be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

That which is claimed:
 1. A method of operating a node of a wirelesscommunications network, the method comprising: transmitting informationto a user equipment over an aggregated carrier that includes a primarycarrier that comprises a first set of primary carrier time/frequencyresources and a secondary carrier that comprises a second set ofsecondary carrier time/frequency resources; and transmittingsynchronization signals and/or reference symbols to the user equipmenton the secondary carrier less often than on the primary carrier.